Method and apparatus for producing and threading a helix into a stack of sheets

ABSTRACT

A method and apparatus for automatically producing and threading a helix into a perforated stack of sheets to form a notebook, calendar or the like. The apparatus comprises a device for continuously winding a thread or wire into a helix, a device for repeatedly cutting the helix to a desired length and a device for threading the cut-to-length helix into a perforated stack of sheets. According to the invention, the cutting device includes a screw-shaped guide, arranged some distance away from the winding device, for longitudinally guiding the helix which is continuously produced by the winding device. At the end of the guide there is located a recess. A movable tool, a portion of which is arranged to fit into the recess, is provided to cut and thereafter bend over a short length of the thread of the helix. The tool is driven in dependence upon the drive of the winding device so that the helix which is continuously produced is repeatedly cut to a desired length.

United States Patent Negro 1 Sept. 5, 1972 [54] METHOD AND APPARATUS FOR PRODUCING AND THREADING A HELIX INTO A STACK OF SHEETS [72] Inventor:

[73] Assignee: Bielomatik Leuze & Co., 3, Neuffen,

Germany [22] Filed: Aug. 21, 1970 [21] Appl. No.: 65,761

Guido Negro, Neufien, Germany [30] Foreign Application Priority Data Aug. 30, 1969 Germany ..P 19 44 223.0

[52] US. Cl. ..140/92.4, 72/130, 140/927 [51] Int. Cl. ..B2lf 3/02 [58] Field of Search ..140/1, 92, 92.3, 92.4, 92.7, 140/929, 92.93; 72/130, 132, 137; 29/227,

[56] References Cited UNITED STATES PATENTS 2,177,054 10/1939 Cau'ni ..140/92.93 2,937,688 5/1960 140 ..92.7

2,735,454 2/1956 Forster ..140/1 Primary Examiner-Lowell A. Larson Attorney-Brumbaugh, Graves, Donohue & Raymond [57] ABSTRACT A method and apparatus for automatically producing and threading a helix into a perforated stack of sheets to form a notebook, calendar or the like. The apparatus comprises a device for continuously winding a thread or wire into a helix, a device for repeatedly cutting the'helix to a desired length and a device for threading the cut-to-length helix into a perforated stack of sheets. According to the invention, the cutting device includes a screw-shaped guide, arranged some distance away from the winding device, for longitudinally guiding the helix which is continuously produced by the winding device. At the end of the guide there is located a recess. A movable tool, a portion of which is arranged to fit into the recess, is provided to cut and thereafter bend over a short length of the thread of the helix. The tool is driven in dependence upon the drive of the winding device so that the helix which is continuously produced is repeatedly cut to a desired length.

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his ATTORNEYS GUID NIEGRO @WMJWQ Q40?! f ZAyaI/d METHOD AND APPARATUS FOR PRODUCING AND THREADING A HELIX INTO A STACK OF SHEETS BACKGROUND OF THE INVENTION The present invention relates to a method and apparatus for automatically producing and threading a helix into a pre-perforated stack of sheets. The helix is formed by a thread, wire or the like and is cut to length and threaded into a line of pre-cut holes in the stack of sheets.

Stacks of sheets which are held together by a spiral and helix are commonly used as notebooks, stenographers pads, calendars and the like. Ordinarily, such books or pads are manufactured in several operations or stages at separate working stations. Usually the stations include a receiving station, an alignment station and a helix insertion station. The helix insertion station is provided with a winding tool which winds the helix and rotates or threads it into the book or pad with the aid of a brake motor; that is, a motor which may be frequently switched on and off and thereby quickly accelerated to or decelerated from its rated speed (approximately 6,500 rpm). The helix is threaded into the stack by means of pivoting guide rollers. Thereafter, the brake motor of the winding tool is braked to a stop, the helix is cut and both its ends are bent over to prevent the helix from threading out.

This known arrangement cannot be readily modified to increase the rate of production. Since the winding tool can be operated only during the period in which the stack of sheets is ready, at the helix insertion station, for helix insertion, and cannot be operated during the time required to cut off and bend over the ends of the helix, the actual helix formation and insertion must be carried out during a very short period of time.

ln practice, control of the production processes described above is effected in a helixing machine by means of a timed shaft which makes one revolution per operation or machine cycle. The actual helixing process-that is, the start of the winding tool, the formation and threading of the helix into the stack of sheets and the braking of the winding tool-takes place while the shaft rotates through an angle of only about 200 or about 55 percent of one complete rotation or one cycle. Thus, if the machine is set to operate at 30 cycles per minute, the formation and threading of each helix must be accomplished in only slightly more than one second.

Attempts to increase the rate of production by employing a more powerful brake motor have been unsuccessful since a brake motor with greater power exhibits naturally a greater angular momentum. An increase in power thus results in a reduction, rather than an increase in the switching speed of the motor.

Attempts have also been made to employ either a mechanical or an electromechanical clutch and brake in conjunction with a continuously rotating drive in place of the brake motor. This arrangement has proved unsatisfactory in practice because the clutch was subject to a high rate of wear due to the frequency with which it was operated.

An additional limit on the rate of production is imposed when plastic coated wire is used to make the helix. At increased speeds of the winding tool, the wire which is being shaped is heated to such a degree that the plastic coating scales off and disrupts the operation of the machine.

SUMMARY OF THE INVENTION An object of the present invention, therefore, is to provide a method and apparatus for automatically producing and threading a helix into a perforated stack of sheets which permits a higher cycle rate than has previously been possible with the methods and apparatus of the prior art.

This object, as well as other objects which will become apparent in the discussion that follows, is achieved, according to the present invention, by continuously forming the helix in a winding device, repeatedly cutting the helix to a desired length and bending over one end thereof prior to insertion into the perforated stack of sheets.

More particularly, the method according to the present invention includes the process of continuously winding a thread into a helix and allowing the helix to extend over a free path without longitudinal guidance and then enter a guide which provides support during cutting and bending. The continuously generated helix is periodically cut to a desired length and the advance end thereof is bent substantially inward toward the helix interior. The cut-to-length helix is then conveyed, unbent end first, to a threading device which inserts it into the perforated stack of sheets. The bent over portion of the bent end of the cut-to-length helix is eventually caused strike against a stop when the threading is complete.

The apparatus according to the present invention for forming and threading the helix into a perforated stack of sheets operates to carry out the method described above. This apparatus is provided with a continuously operated winding or forming device; means for cutting the helix to the desired length; and a threading device for inserting the helix into the perforations of the stack of sheets. The cutting device includes the stationary screw-shaped or helical guide which is arranged at some distance from the winding device to allow the continuously generated helix to initially pass through a buffer zone. The screw-shaped guide is provided with a recess into which is periodically rotated a cutting and bending tool.

Since the winding device may be operated continuously with the method and apparatus of the present invention either the winding speed may be reduced or the cycle rate of the helixing machine may be increased. Since the repeated starting and braking of the winding tool is no longer necessary, the winding tool can be equipped with the continuous drive in lieu of the expensive and complex brake motor.

The free path or buffer zone between the continuously operating winding device and the cutting means permits the helix to change its shape as required to absorb the differences in speed of the end thereof that is being produced and the end thereof that is being cut and bent.

Wlth the method and apparatus of the present invention the helix may be threaded into the stack of sheets by means of the customary driven guide rollers. The cut-to-length helix should be inserted into this threading device with its unbent end first. After the threading is complete, the bent end may be caused to strike a suitably arranged stop thus preventing possible injury to the stack of sheets by threading the helix too far.

When the threading has been terminated, the guide rollers are pivoted outward to permit removal of the stack of sheets. Since a stop is provided, the exact moment that the rollers are swung outward ceases to be critical. If the outward movement of the rollers is delayed and the rollers attempt to drive the helix after the bent end strikes the stop, the helix will contract until it no longer makes frictional contact with the guide rollers.

After the helix is cut to length but before it is threaded, it must be conveyed to the threading device with its unbent end first. Since the unbent is the end which has last been cut, the cut-to-length helix cannot be simply conveyed forward on the same axis along which it was formed.

There are three preferred techniques according to the present invention, for conveying the cut-to-length helix to the threading device:

1. The helix may be rotated by 180 about an axis transverse to its longitudinal axis and then conducted toward the threading device.

2. The helix may be conducted past the threading device as it is formed and cut to length; conveyed in a direction transverse to its longitudinal axis without changing its relative orientation and then conveyed towards the threading device along the line of its axis.

3. The helix may be temporarily stored in a magazine and then removed as desired and introduced into the threading device.

When a magazine is utilized under the latter altemative, the fullness of the magazine may be continuously scanned or sensed. In this way, the winding, cutting and bending cycle can be controlled in dependence upon the fullness of the magazine.

IN the preferred embodiment of the apparatus according to the present invention, the cutting tool is provided with a cutting edge, which co-operates with the bottom of the recess in the helical guide, for cutting through the advancing thread of the helix. The tool is also provided with a recess, immediately following the cutting edge, and a bending edge which, when arranged in the position for bending, is spaced from the bottom of the recess in the helical guide by a distance approximately equal to the thickness of the thread of the helix.

This cutting tool makes it possible, in a single operation, both to cut a section of the helix to a desired length and to bend the leading edge of the advancing thread of the as-yet-uncut helix. Since this advancing end of the thread will strike against the cutting edge of the cutting tool, the advance of the as-yet-uncut helix will be interrupted briefly during the cutting operation. Due to the buffer zone mentioned above, the as-yetuncut helix will be able to absorb the difference in speed of its two ends by increasing its spring tension. When the cutting edge of the cutting tool moves past the advance end of the thread of the helix, this end of the thread will be forced into the recess of the cutting tool at an increased speed. Immediately thereafter, the bending edge of the cutting tool will move into position to bend over the portion of the end which has entered the recess.

BRIEF DESCRIPTION OF THE DRAWINGS the end of the helical guide employed in the apparatus of FIG. 1.

FIG. 3 is an elevational view of a portion of the cutting tool and helical guide of FIG. 2 arranged in a different relative position.

FIG. 4 is an elevational view of the cutting tool and helical guide of FIG. 2 arranged in still another relative position.

FIG. 5 is a representational diagram of the complete helixing apparatus according to one preferred embodiment of the present invention.

FIG. 6 is a representational diagram of the complete helixing apparatus according to a further embodiment of the present invention.

FIG. 7 is a representational diagram of the complete helixing apparatus according to still another preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments of the present invention will now be described in connection with FIGS. 17 of the drawings.

The apparatus shown in FIG. 1 is provided with a winding device 11 which prepares an endless helix 13 from a wire, a plastic-coated wire or a thread of synthetic material. For the sake of simplicity, all these materials are encompassed in and referred to in this specification by the term thread. The winding device 11 may be of any construction whatever; one whatever; one such suitable device is disclosed and described in the German Pat. No. 1,189,513.

At some distance from the point of egress 14 of the winding device, there is arranged a guide element 15 for the helix 13. The guide element 15 is constructed in the shape of a screw or helix having the same pitch as the helix 13. The guide element 15 thus serves to provide longitudinal guidance to the helix 13 by limiting the movement of the helix to forward advance in a helical groove. Between the exit 14 and the guide element 15, the helix l3 advances without a guide, at least in longitudinal direction, so that the helix can be axially compressed.

At the end of the guide, in the direction of advance, there is arranged a recess 16 which, in the example represented, consists of a milled-out section having depth equal to half the diameter of the screw-shaped guide element 15. The recess 16 mates with a cutting tool 17 which rotates about an axis 18.

FIGS. 2 to 4 show the form of the cutting tool 17. It consists of a comparatively long lever which is provided at its free end with the cutting edge 19. The cutting edge 19 cooperates with the bottom 20 of the recess 16 or, more specifically, with its edge 21. The cutting edge 19 continues in the circumferential direction into the portion 22 from which extends the inclined section 23 toward a recess 24. A projection 25 at the edge of the recess 24 forms a bending edge. The projection 25 is set back from the bottom of the recess 16, the edge 19, and the portion 22 by the thickness of the thread of the helix 13.

The cutting tool 17 is driven by a transmission 26 and a gear 27. The winding device is likewise driven by means of the gear 27. However, a regulating belt drive 28 is inserted between the drive gear 27 and the winding device 11 so that it is possible to vary the length of the helix produced per apparatus cycle (per revolution of the cutting tool).

FIGS. 5 to 7 are diagrammatic illustrations of the winding device 11, the continuously formed helix 13, the guide element and the cutting tool 17. With regards to the operation of the apparatus, which will be explained in detail further on, it should be stated here that the cutting tool 17 simultaneously cuts the helix to size and bends, substantially inward, the foremost end of the helix 13 that continuously emerges from the winding device 11 (see FIG. 4). Thus the bend 29 is always at the front end or in the direction of advance of the cut-to-length helix 13'. For the sake of clarity the bend 29 is represented as being turned backward, instead of inward, in FIGS. 5 to 7.

The helix 13' is conveyed to a threading station 30 in which a stack of sheets 31 is arranged with its row of perforations 32 aligned for threading. Guide rollers 33 and 34, at least one of which is driven, are arranged to wind the helix by turning and advancing it into the row of holes 32. These guide rollers may be constructed in the manner well known in the art. At the start of the threading they are swung inward toward the stack of sheets and at the completion of the threading they are swung away.

FIG. 5 shows that the helix, after it has been cut to size, is turned by 180 about an axis transverse to its longitudinal axis. After this rotation, the bend 29 is at the rearward end of the helix so that the latter can be wound without difficulty into the row of perforations 32. At the threading station 30 there is provided a stop 35 which, during winding, is located within the helix 13'. The stop is mounted to the frame but it is also possible to attach it, for example by means of a holder 36, to the guide roller 34.

In the embodiment shown in FIG. 6, the helix runs past and parallel to the threading station; i.e., essentially parallel to the guide rollers 33 and 34. The threading station 30 is arranged in such a manner that not be stopped temporarily as would otherwise be necessary, for example, if the winding device were interrupted in order to insert into it a new coil of wire. This advantage of continuing operation also applies where the winding device and the cutting tool are driven in timed relation to the cycles of the remainder of the machine.

The magazine 39 may be provided with a feeler or scanner device 41 which may operate in any well known manner; e.g., optically or mechanically. This scanning device, which produces either an electrical or a mechanical signal in dependence upon the fullness of the magazine, is connected to a conventional control device 42 which regulates the speed of the winding device 11. Regulation may be effected infinitely variably, stepwise or intermittently.

The apparatus according to the present invention represented in FIGS. 1-7, operates as follows:

When the winding device 11 is driven by the gear 27 and the control drive 28, it forms a continuous-i.e., endless-helix 13 of the thread (wire) 12 supplied to it. The helix advances between the exit 14 of the winding device and the entrance to the guide element 15 over a section or path 40 which provides no longitudinal guidance and thus acts as a buffer zone. The helix subsequently enters and is longitudinally guided by the screw-shaped stationary guide element 15. After a sufficient length of helix has left the guide element at the recess 16, the cutting tool 17, which is driven counterclockwise (as seen in FIGS. 2-4) by the transmission 26, completes one revolution. The cutting edge 19 of the cutting tool cooperates with the edge 21 of the recess 16 to cut off the thread 12. The cut-off helix 13' is indicated in FIG. 2 by the dotted dashed lines.

While the cutting edge 19 and the portion 22 of the cutting tool pass by the thread 12, the rotation and advance of the continually formed helix is interrupted. This temporary stoppage of the helix in the area of the cutting device is absorbed by the portion of the helix in the buffer zone 40. Thus, as new helical turns are continuously being formed by the winding device, the helix is axially compressed and radially somewhat expanded. When the cutting tool has moved to the position shown in FIG. 3, the helix jumps with increased speed into the recess 24 so that its end 29 is placed in front of the projection 25.

As shown in FIG. 4, the end 29' is pressed by the proits threading device threads counter to the direction of jection 25 around the edge 21 of the bottom 20 of the advance of the helix 13 from the winding device 11. It is apparent that the cut-to-length helix 13' points with its unbent end 37, which is to be inserted into the stack first, in the direction of threading device so that it must be only somewhat displaced in the direction shown by the arrow 38. In this embodiment, the rotation by 180 is not required.

In the embodiment shown in FIG. 7, the cut-tolength helix 13' is placed in intermediate storage in a magazine 39. One helix per machine cycle is taken out of the magazine 39 and conveyed to the guide rollers 33, 34 for threading into a stack of sheets. In this embodiment the winding device 11 may be driven independently of the rest of the threading machine. Thus, the gear 27 may be driven by the machine or by a separate motor. Since a given number of helices is always available in this embodiment, the machine need recess 16 to form the bend 29. During the time required for bending (FIG. 4), the helix is again stopped and the buffer zone again prevents an interruption in the advance of the helix from the winding device 11. After the cutting tool 17 has released the bend 29, the helix 13 again freely leaves the guide element 15 until the cutting tool returns to the position shown in FIG. 2. It may be observed that by changing the ratio of the number of revolutions of the cutting tool to the number of revolutions of the winding device, it is possible to change the length of the helices that are cut.

The cut-to-length helix 13' thus produced is next conveyed to the threading station 30. The basic principles of the conveyance have already been described in connection with FIGS. 5 to 7. It should be added that the bend 29 will ensure safe threading of the spiral into the row of holes 32. After the spiral has been threaded into the stack of sheets by the guide rollers 33 and 34 which were previously swung into position, the bend 29 will strike the stop 35. Suitably, the stop 35 is arranged in the area of the first hole of the row of holes 32 so that the helix will be wound into the stack to an exactly defined point. Even if the guide rollers are not swung back in time and attempt to continue threading of the helix, the helix is prevented from advancing into the stack of sheets. Thereafter since the helix, being driven, is extended and thus reduced in diameter, there will no longer be any transmission of the driving force from the guide rollers to the helix thread.

The stop 35 does not interfere in any way with the threading of the helix since the stop is placed in the empty helix interior. The stop holder or support 36 also fails to interfere as it always is situated in the free space between windings. The support further provides the advantage of requiring the helix to enter only in an exactly determined axial position. The support 36 is therefore aligned in a position such that the axial position of the helix will correspond to the position of the row of perforations 32.

Due to the fact that the winding device can always work continually, the present invention permits the winding device to run at a slower speed while the cycle rate of the machine is maintained or, instead, to run at the same speed as it does in prior art machines while the cycle rate is raised. The continuous operation of the winding device also results in a considerable reduction in wear and tear and a simplification of the mechanical structure.

As has been stated above, the helix travels essentially without longitudinal guidance i.e., a longitudinal guide element-in the path 40 designated as the buffer zone. It will be appreciated, however, that some guidance may be necessary to prevent the helix from buckling. In most cases, the helix will have sufficient stiffness to resist buckling and will consequently require no guidance at all.

It will be understood that the method and apparatus according to the present invention is susceptible to various modifications, changes and additions as will occur to those skilled in the art. It is therefore intended that the scope of the invention be limited only by the following claims.

lclaim:

l. A method for automatically producing and threading a helix into a perforated stack of sheets, comprising the steps of:

a. continuously winding a thread into a helix;

b. extending said helix in its longitudinal direction along a free path without longitudinal guidance;

c. guiding said helix in said longitudinal direction along a second path at the end of, and on a common axis with said free path;

. periodically cutting said helix to a desired length at the end of said second path;

e. bending the advance end of the thread of the asyet-uncut helix substantially inward toward the interior of said helix at the end of said second path;

f. conveying the cut-to-length helix, unbent end first,

to an automatic threading device; and

automatically threading said cut-to-length helix, unbent end first, into a perforated stack of sheets until the bent-over portion of the bent end thereof strikes against a stop.

2. The method defined in claim 1, wherein said conveying step includes the step of rotating said cut-tolength helix by 180 about an axis transverse to its longitudinal axis.

3. The method defined in claim 1, wherein said conveying step includes the steps of moving said cut-tolength helix first in a direction transverse to its longitudinal axis and then, unbent end first, in the direction of its longitudinal axis.

4. The method defined in claim 1, wherein said conveying step includes the steps of supplying said cut-tolength helix to a magazine for temporary storage and successively removing a cut-to-length helix from said magazine as required for supply to said threading device.

5. The method defined in claim 4, further comprising the step of sensing the fullness of said magazine and controlling the winding, cutting and bending cycle in dependence upon said fullness.

6. The method defined in claim 1, wherein said cutting and bending steps are effected by a common tool.

7. The method defined in claim 6, wherein the advancing movement of said advance end is inhibited by the cutting edge of said tool .during said cutting step and said as-yet-uncut helix is thereby placed under stress; wherein said advance end is thereafter inserted into a recess in said tool with the force produced by said stress; and wherein said advance end is thereafter bent substantially inward by a bending edge of said tool arranged adjacent to said recess.

8. In apparatus for automatically producing and threading a helix into aperforated stack of sheets which includes means for continuously winding a thread into a helix; means for repeatedly cutting said helix to a desired length; and means for threading the cut-to-length helix into a perforated stack of sheets, the improvement wherein said cutting means includes helical guide means, arranged at a bufi'er distance from said winding means, for guiding the helix in its longitudinal direction, said guide means having a recess therein; tool means, arranged to fit into the recess in said guide means, for cutting said helix to said desired length and bending the advance end of the thread of the as-yet-uncut helix substantially inward toward the interior of said helix and means for driving said tool means in dependence upon the drive of said continuous winding means and said desired length.

9. The improvement defined in claim 8, wherein said tool means includes:

1. a cutting edge, arranged to cooperate with the bottom of the recess in said guide means for cutting through the advancing thread of said helix;

2. a recess, arranged adjacent to said cutting edge, for receiving a section of the advancing thread of said helix; and

3. a bending edge, arranged to cooperate with the bottom of the recess in said guide means, for bending over said section of thread received by the recess in said tool means.

10. The improvement defined in claim 9, wherein said bending edge, when in the position for bending said thread, is spaced from the bottom of the recess in said guide means by a distance approximately equal to the thickness of said thread;

9 19. 11. The improvement defined in claim 9, wherein ing the bent-over end of said cut-to-length helix said tool means is rotatable and said means for driving when the threading is completed. said tool means includes means for rotating said tool 13, Th i provement defined in claim 12, wherein t d f d l 8 h said threading means further includes means for supe appara us e me "1 c aim w erem sai heading means includes: porting said stop means, said supporting means being L apluramy ofdriven guide rollers and arranged to guide the insertion of said cut-to-length 2. stop means, arranged between said rollers at the helix into Sald perforated Stack ofsheets point at which the threading is begun, for contact- 

1. A method for automatically producing and threading a helix into a perforated stack of sheets, comprising the steps of: a. continuously winding a thread into a helix; b. extending said helix in its longitudinal direction along a free path without longitudinal guidance; c. guiding said helix in said longitudinal direction along a second path at the end of, and on a common axis with said free path; d. periodically cutting said helix to a desired length at the end of said second path; e. bending the advance end of the thread of the as-yet-uncut helix substantially inward toward the interior of said helix at the end of said second path; f. conveying the cut-to-length helix, unbent end first, to an automatic threading device; and g. automatically threading said cut-to-length helix, unbent end first, into a perforated stack of sheets until the bent-over portion of the bent end thereof strikes against a stop.
 2. The method defined in claim 1, wherein said conveying step includes the step of rotating said cut-to-length helix by 180* about an axis transverse to its longitudinal axis.
 2. a recess, arranged adjacent to said cutting edge, for receiving a section of the advancing thread of said helix; and
 2. stop means, arranged between said rollers at the point at which the thReading is begun, for contacting the bent-over end of said cut-to-length helix when the threading is completed.
 3. a bending edge, arranged to cooperate with the bottom of the recess in said guide means, for bending over said section of thread received by the recess in said tool means.
 3. The method defined in claim 1, wherein said conveying step includes the steps of moving said cut-to-length helix first in a direction transverse to its longitudinal axis and then, unbent end first, in the direction of its longitudinal axis.
 4. The method defined in claim 1, wherein said conveying step includes the steps of supplying said cut-to-length helix to a magazine for temporary storage and successively removing a cut-to-length helix from said magazine as required for supply to said threading device.
 5. The method defined in claim 4, further comprising the step of sensing the fullness of said magazine and controlling the winding, cutting and bending cycle in dependence upon said fullness.
 6. The method defined in claim 1, wherein said cutting and bending steps are effected by a common tool.
 7. The method defined in claim 6, wherein the advancing movement of said advance end is inhibited by the cutting edge of said tool during said cutting step and said as-yet-uncut helix is thereby placed under stress; wherein said advance end is thereafter inserted into a recess in said tool with the force produced by said stress; and wherein said advance end is thereafter bent substantially inward by a bending edge of said tool arranged adjacent to said recess.
 8. In apparatus for automatically producing and threading a helix into a perforated stack of sheets which includes means for continuously winding a thread into a helix; means for repeatedly cutting said helix to a desired length; and means for threading the cut-to-length helix into a perforated stack of sheets, the improvement wherein said cutting means includes helical guide means, arranged at a buffer distance from said winding means, for guiding the helix in its longitudinal direction, said guide means having a recess therein; tool means, arranged to fit into the recess in said guide means, for cutting said helix to said desired length and bending the advance end of the thread of the as-yet-uncut helix substantially inward toward the interior of said helix and means for driving said tool means in dependence upon the drive of said continuous winding means and said desired length.
 9. The improvement defined in claim 8, wherein said tool means includes:
 10. The improvement defined in claim 9, wherein said bending edge, when in the position for bending said thread, is spaced from the bottom of the recess in said guide means by a distance approximately equal to the thickness of said thread.
 11. The improvement defined in claim 9, wherein said tool means is rotatable and said means for driving said tool means includes means for rotating said tool means.
 12. The apparatus defined in claim 8, wherein said threading means includes:
 13. The improvement defined in claim 12, wherein said threading means further includes means for supporting said stop means, said supporting means being arranged to guide the insertion of said cut-to-length helix into said perforated stack of sheets. 